Other Parts Discussed in Thread: LM46001, , TPS7A47
I'm easily confused, so please bear with me. I'm trying to perform an analysis on a circuit that uses a LM46001AQPWPTQ1. I've read the datasheet multiple times and tried to apply the recommended formulas, but I still come away with questions. The designer used a 1nF capacitor on the SS/TRK pin, this appears to fly in the face of what he datasheet states, so, what is the real affect of placing a small cap to ground on this pin?
I also tried to calculate the output ripple and came up with a number ~20 smaller than what WEBENCH calculated (which used a slightly different LM46001 part), FS=500kHz, D=21%, VIN=28, VOUT=6, L=33µH, COUT=58µF.
Using same values, I also calculated a crossover frequency ~1/3 of what WEBENCH calculated.
I need to understand these differences to ensure I'm not going down the primrose path on the analysis, so any enlightenment is much appreciated.
I'm trying to run the analysis for worst case parameters, and, near as I can tell, WEBENCH is limited such that I cannot use it (output capacitance created using 5 caps, won't let me attach CSS, constrains what caps I can use, tries to optimize when I don't want it optimized)